Methods for optimal multi-channel assignments in vehicular ad-hoc networks

ABSTRACT

A communications path is established among an ordered sequence of moving nodes, representing vehicles. Available channels may differ from one node to the next node and a node cannot use the same channel for both receiving and transmitting information. Three methods are described that provide an optimal sequence of channel assignments between the nodes. A sequence of channel assignments is called optimal if it establishes a communications path from the first node in the sequence to the last node in the sequence, or, if such a path does not exist, from the first node to the farthest node possible in the sequence. The first method uses a depth-first search starting from the first node in the sequence. The second method uses a “look ahead” scheme in the depth-first search method. The third method requires only a single pass through the sequence of nodes by identifying optimal channel assignments in subsequences of nodes without a need for backtracking.

FIELD OF INVENTION

The present invention relates to channel assignments in mobile ad-hocnetworks and more specifically, the invention concerns assignment ofchannels in ad-hoc vehicular networks comprising an ordered sequence ofmoving vehicles.

BACKGROUND OF THE INVENTION

A mobile ad-hoc network (MANET) is formed by multiple moving nodesequipped with wireless transceivers. The mobile nodes communicate witheach other through multi-hop wireless links, wherein every node cantransmit and receive information. Mobile ad-hoc networks have becomeincreasingly important in areas where deployment of communicationsinfrastructure is difficult. Such networks are used for communicationsin battle fields, natural disasters, fleets on the ocean, and so forthNumerous papers have been published on this topic. For example, C. Xu,K. Liu, Y. Yuan, and G. Liu, “A Novel Multi-Channel Based Framework forWireless EEE 802.11 Ad Hoc Networks”, Asian Journal of InformationTechnology, 5, 44-47, 2006 describe a framework for multi-channelmanagement in such networks.

A vehicular ad-hoc network (VANET) refers to a mobile ad-hoc networkdesigned to provide communications among nearby vehicles and betweenvehicles and nearby fixed equipment. W. Chen and S. Cai, “Ad HocPeer-to-Peer Network Architecture for Vehicle Safety Communications”,IEEE Communications Magazine, 100-107, April 2005 present backgroundmaterial and a networking approach that uses local peer grouparchitecture in order to establish communications among vehicles.

The use of multiple channels allows for simultaneous communicationsamong a network of moving nodes, representing vehicles, and increasesthe network throughput. Existing channel assignment methods usedistributed decisions wherein each node determines which channel to usebased on local information on channel availability at neighboring nodes.

The present invention focuses on establishing a communications pathamong an ordered sequence of moving nodes, representing vehicles. Theordered sequence of nodes can be viewed as a directed linear treetopology where a link interconnects a node only to its successor node inthe ordered sequence. A channel is used to send information from onenode to the next on a wireless link. The set of available channels maydiffer from one node to the next due to external interferences, otherongoing communications that involve some of these nodes, differentequipment used at the nodes, and the like. Each of the availablechannels at a node can be used for receiving information from itspredecessor node in the sequence or for transmitting information to itssuccessor node in the sequence. However, the same channel cannot be usedat a node for both receiving information from its predecessor node andtransmitting information to its successor node in the ordered sequenceof nodes. Note that the channel used to transmit information from somenode is the channel used to receive information at its successor node inthe ordered sequence of nodes. The first node in the sequence, or somenearby system, has as input the information of the set of availablechannels at each of the nodes in the ordered sequence. The inventionprovides methods that determine an optimal sequence of channels assignedto the wireless links that interconnect the ordered sequence of nodes. Asequence of channel assignments is called optimal if it establishes acommunications path from the first node in the ordered sequence of nodesto the last node in that sequence, or, if such a path does not exist, itestablishes a communications path from the first node to the farthestnode possible.

The invention uses global information from all nodes in the sequence tocome up with a globally optimal sequence of channel assignments. Currentsystems use distributed methods wherein each node selects a channel fortransmitting information using information from only a subset of nodes.

SUMMARY OF INVENTION

The present invention focuses on establishing a communications pathamong an ordered sequence of moving nodes, representing vehicles. Thesequence of nodes can be viewed as a directed linear tree topology wherea link interconnects a node only to its successor node in the orderedsequence. A channel is used to send information from one node to thenext node on a wireless link. The set of available channels may differfrom one node to the next node. Each of the available channels at a nodecan be used for receiving information from its predecessor node in thesequence or for transmitting information to its successor node in thesequence. However, the same channel cannot be used at a node for bothreceiving and transmitting information. Using information regarding theset of available channels at each of the nodes in the ordered sequenceof nodes, the invention provides methods that determine an optimalsequence of channels assigned to the wireless links connecting thenodes. A sequence of channel assignments is called optimal if itestablishes a communications path from the first node in the orderedsequence to the last one, or, if such a path does not exist, itestablishes a communications path from the first node in the orderedsequence to the farthest node possible. The present invention describesthree methods that find an optimal sequence of channel assignments. Thefirst method uses a depth-first search starting from the first node inthe sequence. The second method improves upon the channel selection rulein a node by using a “look ahead” scheme that may reduce thecomputational effort of the depth-first search method. The third methodrequires only a single pass through the sequence of nodes by identifyingoptimal channel assignments in subsequences of nodes without a need forbacktracking, resulting in computational effort that is proportional tothe number of nodes in the ordered sequence of nodes.

The present invention will be more clearly understood when the followingdescription is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an ordered sequence of nodes, shown as a directedlinear tree network, and the sets of available channels.

FIG. 2 shows an example of the Depth-First Search Method.

FIG. 3 shows an example of the Enhanced Depth-First Search Method.

FIG. 4 shows an example of the One Path Method.

DETAILED DESCRIPTION

Referring now to the figures and FIG. 1 in particular, there is shown anexample 100 of an ordered sequence of five nodes 101-105, also labeledas nodes 1-5. The nodes represent moving vehicles and the links 106-109represent wireless links interconnecting the nodes. For example, link106 connects node 1 to node 2, link 107 connects node 2 to node 3, andso forth. Note that the network comprising the nodes and links can beviewed as a directed linear tree. Each node has a set of channelsavailable for receiving or transmitting information where the termchannel is used as a logical entity. It may represent a frequency band(under FDMA), an orthogonal code (under CDMA), and the like. The set ofavailable channels may differ from one node to the next due to externalinterferences, other ongoing communications that involve some of thesenodes, different equipment used at the nodes, and so forth. For example,node 1 (101) can use channels 1 and 2, as depicted by the set S₁={1, 2},node 2 (102) can use channels 1, 2 and 4 as depicted by the set S₂={1,2, 4}, and so forth. The information of all sets S_(i), i=1, 2, 3, 4 and5 is provided as input to the channel assignment methods. Typically, theinput will be available at node 1, however, it may be available at someother location, e.g., at nearby fixed devices. The channel assignmentmethods are generic and independent of the location of the input. Theobjective is to establish, if possible, a communications path thatconnects node 1 to node 5. If such a communications path cannot beestablished, the objective is to establish a communications pathstarting at node 1 to the farthest node along the ordered sequence ofnodes. Node i may use for receiving or transmitting information onlychannels included in the set S_(i), and the channel selected on theincoming link into node i must differ from that selected on the outgoinglink from node i.

The invention provides three methods that find an optimal sequence ofchannels assigned to the interconnecting links wherein an optimalsequence of channels establishes a communications path from node 1 tothe farthest possible node along the ordered sequence of nodes. Thefarthest node may be node N or some node i<N. Each of the methodsprovide an optimal sequence of channels, however, they may requiredifferent computational effort.

Let S_(i) denote the set of available channels at node i where the setsSi for i=1, 2, . . . , N are provided as input for an ordered sequenceof N nodes. Let T_(i) denote the set of available channels at node i andat node i+1, i.e., T_(i)=S_(i)∩S_(i+1). The sets T_(i) for i=1, 2, . . ., N−1 are readily computed from the sets S_(i) for i=1, 2, . . . , N.Since node i must use on its outgoing link a channel that is in S_(i)and node i+1 must use on its incoming link a channel that is in S_(i+i),node i can interconnect with node i+1 only on channels that are in theset T_(i). Let f_(i) denote the channel used for transmission from nodei to node i+1. In addition, node i must use different channels forreceiving information from node i−1 and for transmitting information tonode i+1. Let FEAS_(i) denote the set of channels that can be used totransmit information from node i and received by node i+1, given thatnode i−1 communicates with node i on channel f_(i−1). Thus, FEAS₁=T₁ andFEAS_(i)=T_(i)−f_(i−1) for i>1. Note that if each of the sets T_(i) hastwo or more channels, a sequence of channels that connects node 1 tonode N can trivially be assigned through arbitrary selection, startingfrom node 1. The challenge is to determine optimal assignments when someof the sets T_(i) include only one channel. Obviously, if some T_(i)does not include any channel, a feasible communications path cannot beestablished beyond that node.

The Depth-First Search Method (DFSM)

Referring now to FIG. 2, there is shown an example of the Depth-FirstSearch Method (DFSM) 200 applied to the ordered sequence of five nodesdescribed in connection with example 100 with S₁={1, 2}, S₂={1, 2, 4},S₃={1, 3}, S₄={1, 3, 4}, and S₅={1, 2}. The DFSM method computes fromthe sets S_(i) the sets T_(i)=S_(i)∩S_(i+1), in particular, T₁={1, 2},T₂={1}, T₃={1, 3}, and T₄={1}. The method builds a search tree asfollows. The method starts with node 1 (201), selecting a channel fromthe set T₁ as the candidate channel on the link from node 1 (201) tonode 2 (202), using some specified rule, e.g., random selection, thelargest or smallest channel index, and so forth. Suppose the methodselects channel 1, as depicted by 203. Channel 1 is now deleted from theset T₂ since the channel used on the outgoing link from node 2 mustdiffer from the channel used on the input to the node, i.e., channel 1.Since the set T₂ is now empty, there is no available channel to connectnode 2 (202) to node 3 (204). So the search on this branch of the treefailed as depicted by 205.

The method then backtracks from 202 to 201 and channel 1 is deleted fromset T₁. The method now selects the remaining channel in T₁, i.e.,channel 2, to connect node 1 (201) to node 2 (206) as depicted by 207.

Since channel 2 is not in T₂, the set T₂ remains unchanged. Next, themethod selects channel 1, as depicted by 209 to connect node 2 (206) tonode 3 (208). Channel 1 is deleted now from T₃ and, as depicted by 211,the method selects channel 3 (211) to connect node 3 (208) to node 4(210). Since channel 3 is not in T₄, the set T₄ remains unchanged. Themethod now selects channel 1, as depicted by 213 to connect node 4 (210)to node 5 (212).

The method succeeded in finding an optimal sequence of channels thatestablishes a communications path that connects node 1 to node 5. Thepath uses channel 2 on the link from node 1 to node 2, channel 1 on thelink from node 2 to node 3, channel 3 on the link from node 3 to node 4,and channel 1 on the link from node 4 to node 5.

The Depth-First Search Method, referred to as DFSM, is summarized asfollows:

  DFSM Initialization   Compute sets T_(i) = S_(i) ∩ S_(i + 1) for i =1, 2, ..., N − 1.   N ← minimum[N, smallest i with T_(i) = Ø] (acommunications path cannot be   established from node 1 to a node beyondthe revised N).   Initialize sets TEMP = BEST = Ø (TEMP is the interimsequence of channels   from node 1 to the currently reached node, andBEST records the longest sequence   of channels found since thebeginning of the search).   Initialize i = 1. End of initialization.While i < N   FEAS_(i) = T_(i) − f_(i − 1) ( for i = 1, FEAS_(i) =T_(i)).   If FEAS₁ = Ø, STOP (the set BEST provides the longest possiblesequence of   channels; at this stopping point the optimalcommunications path does not reach   node N).   If FEAS_(i) = Ø (i > 1),backtracking is needed:   Begin     If the sequence of channels in TEMPis longer than that in BEST,     then BEST ← TEMP.     Update T_(i − 1)← T_(i − 1) − f_(i − 1).     Update TEMP ← TEMP − f_(i − 1).     Updatei ← i − 1.     Go to beginning of the while loop.   End.   FEAS_(i) ≠ Ø:Select channel on next link.   Begin     Select channel f_(i) ∈ FEAS_(i)for transmitting from node i to node i + 1     using an arbitrary rule(e.g., random selection).     Update TEMP ← TEMP + f_(i).     Update i ←i + 1.   End. End of while loop. BEST ← TEMP (at this stopping point theset BEST provides a communications path that connects node 1 to node N).STOP. End of DFSM.

The Enhanced Depth-First Search Method (EDFSM)

Referring now to FIG. 3, there is shown an example of the EnhancedDepth-First Search Method (EDFSM) 300 applied to the same orderedsequence of five nodes described in example 100 with S₁={1, 2}, S₂={1,2, 4}, S₃={1, 3}, S₄={1, 3, 4}, and S₅={1, 2}. The method computes fromthe sets S_(i) the sets T_(i)=S_(i)•S_(i+1), in particular, T₁={1, 2},T₂={1}, T₃={1, 3}, and T₄={1}. EDFSM builds a search tree in the sameway as DFSM. However, EDFSM uses a “look-ahead” rule to select a channelfrom the channels in the set FEAS_(i). The EDFSM method first examineswhether the set FEAS_(i) includes a channel that is not in the setT_(i+1), and if so it selects such a channel. Note that selecting such achannel does not decrease the selection options FEAS_(i+1) at node i+1.If such a channel does not exist, the same rule used in DFSM will beused.

Referring to FIG. 3, the method starts with selecting a channel from theset FEAS₁=T₁ as the candidate channel on the link from node 1 (301) tonode 2 (302). Since channel 2 is the only channel in T₁ that is not inT₂, the method selects channel 2, as depicted by 303, to connect node 1(301) to node 2 (302). Note that by using this “look-ahead” rule we didnot select channel 1 which would lead to a failure to establish aconnection from node 2 to node 3 as previously demonstrated in example200.

The remaining steps of the search in example 300 are the same as thatshown in example 200. Since channel 2 is not in T₂, the set T₂ remainsunchanged. Next, the method selects channel 1, as depicted by 305 toconnect node 2 (302) to node 3 (304). Channel 1 is deleted now from T₃and, as depicted by 307, the method selects channel 3 to connect node 3(304) to node 4 (306). Since channel 3 is not in T₄, the set T₄ remainsunchanged. The method now selects channel 1, as depicted by 309 toconnect node 4 (306) to node 5 (308).

EDFSM succeeded in finding an optimal sequence of channels thatestablishes a communications path from node 1 to node 5. This is thesame sequence found by using the DFSM method in example 200. The pathuses channel 2 from node 1 to node 2, channel 1 form node 2 to node 3,channel 3 from node 3 to node 4, and channel 1 from node 4 to node 5.EDFSM requires, in general, less computational effort than DFSM sincethe “look-ahead” rule may prevent selection of channels that would leadto backtracking on the search tree. Note, however, that EDFSM may stillrequire backtracking. This can be easily demonstrated by adding anothernode, referred to as node 1′, between node 1 and node 2 with the setS_(1′)=S₁. Now, starting at node 1, the “look-ahead” rule does notprovide any guidance at node 1. If channel 2 is selected at node 1,channel 1 must be selected at node 1′, and no channel would be availableto connect node 2 to node 3. Backtracking on the search tree would thenbe required.

The Enhanced Depth-First Search Method, referred to as EDFSM, is asfollows:

  EDFSM Initialization   Compute sets T_(i) = S_(i) ∩ S_(i + 1) for i =1, 2, ..., N − 1.   N ← minimum[N, smallest i with T_(i) = Ø] (acommunications path cannot be   established from node 1 to a node beyondthe revised N).   Initialize sets TEMP = BEST =Ø (TEMP is the interimsequence of channels   from node 1 to the currently reached node, andBEST records the longest sequence   of channels found since thebeginning of the search).   Initialize i = 1. End of initialization.While i < N   FEAS_(i) = T_(i) − f_(i − 1) ( for i = 1, FEAS_(i) =T_(i)).   If FEAS₁ = Ø, STOP (the set BEST provides the longest possiblesequence of   channels; at this stopping point the optimalcommunications path does not reach   node N).   If FEAS_(i) = Ø (i > 1),backtracking is needed:   Begin     If the sequence of channels in TEMPis longer than that in BEST,     then BEST ← TEMP.     Update T_(i − 1)← T_(i − 1) − f_(i − 1).     Update TEMP ← TEMP − f_(i − 1).     Updatei ← i − 1.     Go to beginning of the while loop.   End.   FEAS_(i) ≠ Ø:Select channel on next link.   Begin     Select channel for transmittingfrom node i to node i +1 as follows:     If available, select some f_(i)∈ FEAS_(i)\T_(i + 1) (i.e., f_(i) is in FEAS_(i) but not in    T_(i+1)); otherwise, select some f_(i) ∈ FEAS_(i) using an arbitraryrule (e.g.,     random selection).     Update TEMP ← TEMP + f_(i).    Update i ← i + 1.   End. End of while loop. BEST ← TEMP (at thisstopping point the set BEST provides a communications path that connectsnode 1 to node N). STOP. End of EDFSM.

The One-Pass Method (OPM)

Referring now to FIG. 4, there is shown an example 400 of the One PassMethod (OPM) applied to the same ordered sequence of five nodesdescribed in example 100 with S₁={1, 2}, S₂={1, 2, 4}, S₃={1, 3}, S₄={1,3, 4}, and S₅={1, 2}. The method computes from the sets S_(i) the setsT_(i), in particular, T₁={1, 2}, T₂={1}, T₃={1, 3}, and T₄={1}.

Starting from node 1 (401), set T₂={1} is the first set with a singlechannel. Therefore, moving backwards, the method selects channel 1 onthe link from node 2 (402) to node 3 (403), updates T₁ by deletingchannel 1 from T₁, which results in T₁={2}, and selects channel 2 on thelink from node 1 (401) to node 2 (402). The selection of channels onthis subsequence is depicted by 406. Channel 1 is also deleted from setT₃, leading to T₃={3}. The direction of the arrow in 406 emphasizes thatthe subsequence of channels assigned to the links is determinedbackwards, i.e., first for the link connecting node 2 to node 3 and thenfor the link connecting node 1 to node 2.

Next, starting from node 3 (403), T₃={3} is the first set with a singlechannel. Therefore, the second subsequence includes only a single linkand the method selects, as depicted by 407, channel 3 on the link fromnode 3 (403) to node 4 (404). Since T₄ does not include channel 3, noupdate is needed.

Finally, starting from node 4 (404), node 5 (405) is reached. Asdepicted by 408, channel 1 is selected from node 4 (404) to node 5(405).

The OPM method succeeded in finding an optimal sequence of channels thatestablishes a communications path from node 1 to node 5. This is thesame sequence found by DFSM and EDFSM. The path uses channel 2 from node1 to node 2, channel 1 form node 2 to node 3, channel 3 from node 3 tonode 4, and channel 1 from node 4 to node 5.

The OPM method does not build a search tree. Instead, it looks for thefirst node, say node m, along the ordered sequence of nodes that has asingle channel in the set T_(m) and assigns the channel in T_(m) to thelink connecting nodes m to node m+1 The assigned channel is deleted fromset T_(m−1). It then proceeds to node m−1 and arbitrarily assigns achannel from set T_(m−1) to the link connecting node m−1 to node m. Themethod continues in that manner until a channel is assigned to the linkconnecting node 1 to node 2. Assignment of channels to the links alongthe path that connects node 1 to node m+1 is completed. Note that thebackwards assignment of channels to interconnect the subsequence ofnodes 1 to m+1 is guaranteed to succeed since each of the sets T_(i) fori=m−1, m−2, . . . , 1 has at least two channels.

If node m=N−1, the OPM method terminates since a path is establishedfrom node 1 to node N. Suppose m<N−1. The assigned channel on the linkinto node m+1 is deleted from set T_(m+1) and OPM searches for the nextnode in the ordered sequence beyond node m, say node n, that has asingle channel in the set T_(n). OPM then assigns channels to thesubsequence of links that connect node n to node n+1, node n−1 to noden, . . . , node m+1 to node m+2.

The OPM method continues to assign channels to such subsequences until apath that connects node 1 to node N is established or until some set,say T_(p), is encountered with T_(p)=Ø. In the latter case, acommunications path can be established only from node 1 to node p.

Note that a subsequence with node N as its last node may have more thanone channel in T_(N−1), in which case the OPM method arbitrarily assignsone of these channels to the link connecting node N−1 to node N.

The OPM method will find an optimal sequence in an effort that isproportional to the number of nodes, i.e., in an effort of O(N) (aftercomputing the sets T_(i)). The sequence found will generate acommunications path from node 1 to node N, or, if not possible, fromnode 1 to the farthest node possible along the ordered sequence ofnodes.

Let |T_(i)| denote the number of channels in the set T_(i). The One PathMethod, referred to as OPM, is as follows:

  OPM Initialization   T_(i) = S_(i) ∩ S_(i + 1) for i = 1, 2, ..., N− 1.   N ← minimum[N, smallest i with T_(i) = Ø] (a communications path  cannot be established from node 1 to a node beyond the revised N).  MIN = 1. End of initialization. Subsequence Channel Assignment   MAX =[i: Smallest i ≧ MIN with |T_(i)| = 1]; if no |T_(i)| = 1 set   MAX = N− 1.   Select some f_(MAX) ∈ T_(MAX) using an arbitrary rule (e.g.,random   selection).   i = MAX.   While i > MIN     T_(i − 1) ← T_(i −1)− f_(i).     Select some f_(i − 1) ∈ T_(i − 1) using an arbitrary rule(e.g.,     random selection).     i ← i − 1.   End of while loop. End ofsubsequence channel assignment. Termination Checks   MIN ← MAX + 1.   IfMIN = N, STOP (assigned channels f₁, f₂, ..., f_(N − 1) provides   acommunications path from node 1 to node N).   T_(MIN) ← T_(MIN) −f_(MIN − 1).   If T_(MIN) = Ø, STOP (assigned channels f₁, f₂, ...,f_(MIN − 1) provide   a communications path to the farthest nodepossible - node MIN).   Go to beginning of Subsequence ChannelAssignment. End of termination checks. End of OPM.

Suppose channels could be assigned only up to node p<N (the initialvalue of N) using any of the methods DFSM, EDFSM or OPM (all threemethods will establish a communications path to the farthest possiblenode). Since the sets S_(i) may change quite rapidly, it may be desiredto establish a partial path up to node p and re-execute a channelassignment method, starting from node p, after a specified timeinterval. A complete path from node 1 to node N may thus be establishedby combining several partial communications paths established throughsequential executions of a channel assignment method.

The algorithms described above are capable of being performed on aninstruction execution system, apparatus, or device, such as a computingdevice. The algorithms themselves may be contained on acomputer-readable medium that can be any means that can contain, store,communicate, propagate, or transport the program for use by or inconnection with an instruction execution system, apparatus, or device,such as a computer.

While there has been described and illustrated methods for optimalmulti-channel assignments in ad-hoc vehicular networks comprised of anordered sequence of moving vehicles, it will be apparent to thoseskilled in the art that variations and modifications are possiblewithout deviating from the broad teachings and scope of the presentinvention which shall be limited solely by the scope of the claimsappended hereto.

1. A method for assigning channels to wireless links interconnecting anordered sequence of nodes, comprising the steps of: receivinginformation of a set of available channels at each node of an orderedsequence of nodes wherein sets of available channels at each node may bedifferent; and assigning channels to interconnecting links of an orderedsequence of nodes using a non-exhaustive search where the channelassigned to any of the links is selected from among the channelsincluded at the intersection of the sets of available channels at thetwo end-nodes of the respective link, and the channels assigned to anytwo sequential links with a joint node are different; where the assignedchannels to links establish a communications path from the first node ofthe ordered sequence of nodes to the farthest node in the sequence thatcan be reached.
 2. A method as set forth in claim 1, wherein saidassigning channels to interconnecting links of an ordered sequence ofnodes comprises using a search tree as specified by DFSM.
 3. A method asset forth in claim 1, wherein said assigning channels to interconnectinglinks of an ordered sequence of nodes comprises using a search tree asspecified by EDFSM.
 4. A method as set forth in claim 1, wherein saidassigning channels to interconnecting links of an ordered sequence ofnodes comprises using a single pass method through the ordered sequenceof nodes as specified by OPM.
 5. A method as set forth in claim 4,wherein said assigning channels to interconnecting links of an orderedsequence of nodes determines all assigned channels in a computationaleffort that is proportional to the number of nodes in the orderedsequence of nodes.
 6. A method as set forth in claim 1, wherein saidnodes represent vehicles.
 7. A method as set forth in claim 6, whereinsaid assigning channels to interconnecting links of an ordered sequenceof nodes comprises using a search tree as specified by DFSM.
 8. A methodas set forth in claim 6, wherein said assigning channels tointerconnecting links of an ordered sequence of nodes comprises using asearch tree as specified by EDFSM.
 9. A method as set forth in claim 6,wherein said assigning channels to interconnecting links of an orderedsequence of nodes comprises using a single pass method through theordered sequence of nodes as specified by OPM.
 10. A method as set forthin claim 9, wherein said assigning channels to interconnecting links ofan ordered sequence of nodes determines all assigned channels in acomputational effort that is proportional to the number of nodes in theordered sequence of nodes.
 11. A method for establishing acommunications path from a first node in an ordered sequence of nodes tothe farthest possible node in an ordered sequence of nodes in an ad-hocnetwork comprising the steps of: receiving information of a set ofavailable channels at each of the nodes in an ordered sequence of nodeswherein sets of available channels at each node may be different; and;assigning channels to interconnecting links of an ordered sequence ofnodes using a non-exhaustive search where the channel assigned to any ofthe links is selected from among the channels included at theintersection of the sets of available channels at the two end-nodes ofthe respective link, and the channels assigned to any two sequentiallinks with a joint node are different using a method selected from thegroup consisting of a search tree as specified in DFSM, a search tree asspecified by EDFSM, and a single pass method through the orderedsequence of nodes as specified by OPM.
 12. A method as set forth inclaim 11, wherein said assigning channels to the links interconnectingan ordered sequence of nodes is executed multiple times with a specifiedstoppage time from one execution time to the next execution time,wherein communications paths established for subsets of the orderedsequence of nodes are combined to establish a communications path fromthe first node in the ordered sequence of nodes to the farthest possiblenode in the ordered sequence of nodes.
 13. A method as set forth inclaim 11, wherein the nodes represent vehicles.
 14. A system forestablishing a communications path from the first node in an orderedsequence of nodes to the farthest possible node along the orderedsequence of nodes in an ad-hoc network comprising: means for storinginformation of a set of available channels at each node in an orderedsequence of nodes; means for assigning channels to interconnecting linksof an ordered sequence of nodes using a non-exhaustive search where thechannel assigned to any of the links is selected from among the channelsincluded at the intersection of the sets of available channels at thetwo end-nodes of the respective link, and the channels assigned to anytwo sequential links with a joint node are different.
 15. A system asset forth in claim 14, wherein said means for assigning channels tointerconnecting links of an ordered sequence of nodes uses a search treeas specified by DFSM.
 16. A system as set forth in claim 14, whereinsaid means for assigning channels to interconnecting links of an orderedsequence of nodes uses a search tree as specified by EDFSM.
 17. A systemas set forth in claim 14, wherein said means for assigning channels tointerconnecting links of an ordered sequence of nodes uses a single passmethod through the ordered sequence of nodes as specified by OPM. 18.The system as set forth in claim 14, wherein said means for assigningchannels to interconnecting links of an ordered sequence of nodes isexecuted multiple times with a specified stoppage time from oneexecution to the next execution, wherein communications pathsestablished for subsets of the ordered sequence of nodes are combined toestablish a communications path from the first node to the farthestpossible node in the sequence.
 19. A system as set forth in claim 14,wherein said nodes represent vehicles.